This invention relates to plastic or rubber seal disks for seal-type bearings, in particular bearings with seal grooves formed inside each of two shoulders of an outer ring. More specifically, this invention relates to an improved seal disk for bearings that can be fitted into the seal groove concentrically with the bearing and having the bearing axis as center. The seal disk of the present invention prevents enclosed lubricant from leaking out almost infallibly, even when the seal disk expands or shrinks under thermal stress and/or absorbs water or other liquids and swells.
Seal-type bearings with lubricant enclosed therein are widely used in such fields as office equipment and household electric appliances. In bearings of this type, plastic and rubber seal disks are widely used because they provide high sealing performance and easy fitting. Examined Japanese utility model application No. 7-32985 discloses one widely known embodiment thereof.
The seal disk disclosed in Japanese utility model 7-32985 is illustrated in FIG. 19. As shown, the seal disk is integrally formed and has a ring-shaped raised area 6a with a trapezoid-like section on the back side in the outer circumferential portion and a projection 6b with a triangular section on the face in the outer circumferential portion. Seal disk 6 is placed around an inside edge of the face of outer ring 7 and pressed uniformly into the U-shaped groove formed inside each shoulder of outer ring 7, as shown in FIG. 20. Seal disk 6 is caught in groove 7xe2x80x2, with the inside flat top surface of ring-shaped raised area 6a in contact with the inner inside wall of seal groove 7xe2x80x2 and projection 6b bent on the outer inside wall of seal groove 7xe2x80x2.
Thus seal disk 6 is held in seal groove 7xe2x80x2 tightly and firmly by the elastic force of projection 6b, with the gap between the outer ring and the inner ring securely sealed. That is, seal disk 6 has the outer peripheral portion in contact with inner inside wall 7a of seal groove 7xe2x80x2 and elastically with outer inside wall 7b of seal wall 7xe2x80x2, with a minute gap G defined between the bore edge of seal disk 6 and the inner ring. This prevents lubricant enclosed between outer and inner rings 7 and 8 from leaking out and keeps dust and other foreign matter from entering the space between the two rings.
In FIG. 20, reference numeral 9 indicates one of a plurality of free-rolling balls placed between outer and inner rings 7 and 8, while reference numeral 10 is a retainer or separator, keeping balls 9 apart from one another at regular intervals. The bearing in which plastic or rubber seal disk 6 is used has the outer inside wall 7b of seal groove 7xe2x80x2 designed so as to define an angle of inclination a of about 45 degrees with the face of outer ring 7, as indicated in FIG. 21.
With the outer peripheral portion of seal disk 6 held in seal groove 7xe2x80x2 of outer ring 7, projection 6b is bent toward the center of seal disk 6, with an elastic reaction force N working in a direction indicated by the arrow, shown in FIG. 21. A component of this reaction force N works in the direction of the center of seal disk 6 from the circumference thereof. In FIG. 21, the angle of inclination xcex1 of outer inside wall 7b of the seal groove 7xe2x80x2 is large, and so is the component force working from the outer peripheral portion of seal disk 6 toward the bore or the center thereof. As a result, seal disk 6 when installed is automatically concentric with the bearing and has the axis of the bearing as a center. Gap G between the bore wall of seal disk 6 and inner ring 8 is maintained approximately uniform all around.
However, bearings with smaller angles of inclination xcex1 will have smaller component forces working from an outer peripheral portion of seal disk 6 to the bore. When a conventional plastic or rubber seal disk 6 is placed in such a bearing, the elastic reaction force N will work more along the direction of the axis of the bearing, because of the smaller angle of inclination xcex1, as illustrated in FIG. 22.
In bearings with small angles of inclination xcex1 of the outer inside wall 7b of seal groove 7xe2x80x2, the seal disk 6 can fail to be mounted concentrically with the bearing and have the axis as center. That is, a seal disk 6 may be installed eccentrically, with non-uniformity caused in the gap G between the seal disk 6 and the inner ring 8. That can cause such problems as decreased sealing performance, dismounting of seal disk 6 off seal groove 7xe2x80x2, and deterioration in the roundness of outer ring 7.
These problems are especially evident with bearings in which a metallic seal disk or a metal-plastic combination seal disk is used. The seal grooves 7xe2x80x2 in such bearings are designed so that the angle of inclination xcex1 is less than approximately 17 degrees. In such bearings, a plastic or rubber seal cannot be used in place of metallic or metal-plastic combination seal disks, even though plastic and rubber seal disks are less expensive but excellent in durability.
Another problem relates to the lubricant that is normally enclosed within seal disk 6 of the bearing. Rotation of the bearing generates a centrifugal force that forces the lubricant outward. Leakage of the lubricant is blocked primarily by seal disk 6 with its raised area 6a in close contact with the inner inside wall 7a of seal groove 7xe2x80x2. Contact seal performance at this point is a function of the contact pressure, the closeness of the contact, and the size of the contact area. Increasing the contact pressure and the size of the contact area can improve seal performance and minimize the possibility of lubricant leakage. However, there is a certain limit to the magnitude of the elastic reaction force that can be mounted in practice on a raised area 6a, because of such factors as the mechanical strength of the seal disk and the inside edge of the outer ring face as well as the resistance force to be overcome in mounting a seal disk 6. Also, a certain limit is imposed on the size I of the contact area between inner inside wall 7a of seal groove 7xe2x80x2 and raised area 6a, because of the thickness of the bearing outer ring 7, the shape of the seal groove 7xe2x80x2, and other considerations. Thus the size I of the contact area may not be expanded very much.
For those reasons, seal-type bearings using conventional plastic or rubber seals as shown in FIG. 18 cannot completely keep the lubricant from leaking out. The centrifugal force of the rotating outer ring 7 will force some lubricant out of the seal disk 6 through seal groove 7xe2x80x2, although the leakage may be very small. Leakage of the lubricant increases with a rise in the operating temperature of the seal-type bearing, because the viscosity of the lubricant rapidly lowers as the operating temperature exceeds 80xc2x0 C.
A seal disk 6 itself undergoes great change in the crystal structure of its resin material as it is subjected repeatedly to a heating and cooling cycle and as it absorbs moisture from the atmosphere. This results in distortion or a change in dimension of the seal disk, with increased leakage of the lubricant.
The present invention addresses problems such as those described above. It is an object of the present invention to provide a bearing seal disk that can be fixed in the seal groove of an outer ring concentrically with the bearing and have the axis thereof as its center, irrespective of the angle of inclination formed by the outer inside wall of the seal groove in the outer ring. It is another object of the present invention to provide a bearing seal disk the sealing performance of which is so enhance as to prevent lubricant from leaking out almost completely, both in high temperature operation and in and after prolonged service.
To achieve these objects, the present invention provides a non-contact plastic or rubber seal disk for bearings, the disk having an outer peripheral portion to be pushed into a ring-shaped seal groove having a U-shaped section. The seal groove is formed inside each shoulder of the outer ring or outside the outer end of the outer ring land of the bearing and comprises an inner inside wall perpendicular to the axis of the bearing, a bottom wall, and an open-out-formed outer inside wall. The outer peripheral portion of the seal disk is in elastic contact with the inner inside wall and the outer inside wall of the ring-shaped seal groove. The seal disk is configured so as to provide a very narrow gap between the bore wall of the seal disk and the inner ring of the bearing.
The ring-shaped seal groove is provided with a protrusion on the inner inside wall thereof at the outer end of each outer ring land, that is, at each of the edges of the inside wall of the outer ring. On the back side, the seal disk is provided with a ring-shaped raised area with a trapezoid-like section that is brought into area contact with the inner inside wall of the seal groove. On the face, the seal disk has a ring-shaped thin projection, optionally having its tip formed like an arc, in its outer peripheral portion that is brought elastically into contact with the outer inside wall of the seal groove in the outer ring. A ring-shaped sealing recess if formed just inside the trapezoid-like raised area on the seal disk, the recess coming into contact with at least part of the protrusion formed on the inner inside wall of the seal groove.
The seal disk thus configured is pushed into the seal groove, and at least part of the projection in the groove is brought into contact with the sealing recess of the seal disk. In this way, the seal disk is mounted in the bearing concentrically with the bearing axis as its center, which increases sealing performance.
In addition to the structure just described, the non-contact plastic or rubber seal disk for bearings may be provide with a protrusion having a rectangular or trapezoid-like section on the inner inside wall of the seal groove at the outer edge of each outer ring land of the bearing. The sealing recess in the seal disk may be defined by a notch in the shape of a step with a rectangle-like or trapezoid-like section formed just inside the trapezoid-like raised area ring. The seal disk is pushed with the above-mentioned protrusion coming into that step.
The present invention also provides a non-contact plastic or rubber seal disk for bearings having an outer peripheral portion to be pushed into a ring-shaped seal groove of U-shaped section and formed inside each shoulder of the outer ring or at each outer end of each outer ring land of the bearing. The seal groove comprises an inner inside wall perpendicular to the axis of the bearing, a bottom wall, and an open-out-formed outer inside wall. The outer peripheral portion of the seal disk is in elastic contact with the inner inside wall and the outer inside wall of the groove. The seal disk is configured so as to provide a very narrow gap between the bore wall of the seal disk and the inner ring of the bearing.
The ring-shaped seal groove is provided with a sealing pit on the inner inside wall thereof. The seal disk is provided with, on the back side of the outer peripheral portion thereof, a ring-shaped raised area having a trapezoid-like section that comes into area contact with the inner inside wall of the seal groove and, on the face of the outer peripheral portion of the seal disk, a ring-shaped thin projection that comes into contact, in a bent form, with the outer inside wall of the seal groove. In this embodiment, the seal disk is also provided with, on the aforesaid raised area thereof, a protuberance that comes into area contact with at least part of the pit formed on the inner inside wall of the seal groove.
The seal disk so configured is pushed into the seal groove, and at least part of the ring-shaped protrusion in the groove is brought into contact with the sealing recess of the seal disk. In this way, the seal disk is mounted in the bearing concentrically with the bearing axis as its center, and improved seal performance is achieved.
In this embodiment, the sealing pit and the sealing protuberance may be approximately rectangular, semi-circular, V-shaped, or trapezoidal in sectional shape. In any of these configurations, the sealing protuberance may be brought into close contact with the sealing pit. When the sealing protuberance is approximately rectangular, V-shaped, or trapezoidal in sectional shape, the outer side surface of the pit may connect linearly with an inclined insertion surface on the outer peripheral side of the seal disk. Further, in any of these configurations, the thin projection may be one with the tip formed in the shape of an arc.
In addition, the sealing pit 2g may be a recess formed in a step shape at the inside wall (2f) side of the outer ring 2. In this case, leakage of grease is prevented as long as the seal disk is not shrunk due to the temperature rise.